Chapter 4: Energy 

Section 1: The Nature of Energy

• What is energy?
  • Every change that occurs—large or small—involves energy.
  • When something is able to change its environment or itself, it has energy.
  • Energy is the ability to cause change.
  • Energy can be stored and it can move from place to place.
  • Radiant energy from the Sun travels a vast distance through space to Earth, warming the planet and providing energy that enables green plants to grow.
• Kinetic Energy: the energy a moving object has because of its motion.
  • The kinetic energy of a moving object depends on the object’s mass and its speed.
  • Joule: The SI unit of energy
• Potential Energy: Stored energy due to position
  • Energy doesn’t have to involve motion.
  • Elastic Potential Energy: energy stored by something that can stretch or compress, such as a rubber band or spring.
  • Chemical Potential Energy: Energy stored in chemical bonds
  • Gravitational Potential Energy: energy stored by objects due to their position above Earth’s surface.
  • According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground.
  • An object’s gravitational potential energy increases as its height increases.

Section 2: Conservation of Energy

• Changing Forms of Energy
  • A lightbulb is a device that transforms electrical energy into light energy and thermal energy.
  • Fuel stores energy in the form of chemical potential energy.
  • In the engine of a car, several energy conversions occur.
  • Some energy transformations are less obvious because they do not result in visible motion, sound, heat, or light.
• Conversions Between Kinetic and Potential Energy
  • To understand the energy conversions that occur, it is helpful to identify the mechanical energy of a system.
  • Mechanical Energy: the total amount of potential and kinetic energy in a system and can be expressed by this equation.
  • Mechanical energy is energy due to the position and the motion of an object or the objects in a system.
  • Energy transformations also occur during projectile motion when an object moves in a curved path.
  • Objects that can fall have gravitational potential energy.
• The Law of Conservation of Energy: states that energy cannot be created or destroyed.
  • Mechanical energy stays constant.
  • Kinetic and potential energy simply change forms and no energy is destroyed.
  • Energy can change from one form to another, but the total amount of energy never changes.
  • The law of conservation of energy requires that the total amount of energy going into a hair dryer must equal the total amount of energy coming out of the hair dryer.
  • The law of conservation of energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed.
  • Sometimes it is hard to see the law of conservation of energy at work.
  • The total amount of energy always stays the same.
  • A special kind of energy conversion—nuclear fusion—takes place in the Sun and other stars.
  • Mass is converted to energy in the processes of fusion and fission.
  • Another process involving the nuclei of atoms, called nuclear fission, converts a small amount of mass into enormous quantities of energy.
  • In either process, fusion or fission, mass is converted to energy.
  • In processes involving nuclear fission and fusion, the total amount of energy is still conserved if the energy content of the masses involved are included.
  • The process of nuclear fission is used by nuclear power plants to generate electrical energy.
• The Human Body - Balancing the Energy Equation
  • Some of the chemical potential energy stored in your body is used to maintain a nearly constant internal temperature.
  • A portion of this energy also is converted to the excess heat that your body gives off to its surroundings.
  • The complex chemical and physical processes going on in your body also obey the law of conservation of energy.
  • Your body stores energy in the form of fat and other chemical compounds.
  • To maintain a healthy weight, you must have a proper balance between energy contained in the food you eat and the energy your body uses.
  • Your body also can use the chemical potential energy stored in fat for its energy needs.
  • Every gram of fat a person consumes can supply 9 C of energy.